Seriously-
If you're just going to do graphics then I'd say go with OpenGL. It's a little bit easier than DirectGraphics (the graphics API of DirectX). If you plan on making a game or something and only using Windows then go with DirectX because it's a complete multimedia API collection, it has sound, input, video, etc. OpenGL is purely a graphics API so you'll need something else for the rest. I'd recommend Simple DirectMedia Layer. www.libsdl.org The benefit of using SDL is that it's cross platform and you can use OpenGL for it's graphics component. It's a much simpler API than DirectX but not quite as full featured (it's still growing). It should be enough to get you started though (and quickly). Also, there are many extra APIs people have made to fill in what's missing in the core release.

You can find the OpenGL "Red Book" and "Blue Book" online too, so you don't have to pay for them. OpenGL tends to have much more information available than the most current version of DirectX (although the SDK docs are very helpful) and you should use the most current version.